The present invention relates to a cutting tool for metal machining, comprising a substrate of cemented carbide, cermet, ceramics, high speed steel or cubic boronitride and, on the surface of said substrate, a hard and wear resistant refractory coating deposited by Physical Vapor Deposition (PVD). The coating is adherently bonded to the substrate and comprises a laminar, multilayered structure of alternating metal nitrides, metal carbides or metal carbonitrides as individual layers, having an aperiodic structure and an average Si content of from about 1 to about 17 at %.
The methods of depositing a thin refractory coating (from about 1 to about 20 μm) of materials like alumina (Al2O3), titanium carbide (TiC) and/or titanium nitride (TiN) onto, e.g., a cutting tool of cemented carbides, cermets, ceramics, cubic boronitride or high speed steels are well established technologies and the tool life of the coated cutting tool, when used in metal machining, is considerably prolonged. The prolonged service life of the tool may under certain conditions extend up to several hundred percent. Modern commercial cutting tools are characterised by a plurality of layer combinations with double or multilayer structures. The total coating thickness varies between about 1 and about 20 micrometers (μm) and in the prior art, the multilayered structure is characterised in the nanometer (nm) and/or micrometer range (μm), i.e., the thickness of the individual layers varies between a few nanometers and a few hundreds of a nanometers.
There exist several PVD techniques capable of producing refractory thin layers on cutting tools and the most established methods are ion plating, magnetron sputtering, arc discharge evaporation and IBAD (Ion Beam Assisted Deposition). Each method has its own merits and the intrinsic properties of the produced coating such as microstructure/grain size, hardness, state of stress, cohesion and adhesion to the underlying substrate may vary depending on the particular PVD method chosen. An improvement in the wear resistance or the edge integrity of a PVD coated cutting tool being used in a specific machining operation can thus be accomplished by optimizing one or several of the above mentioned properties.
With nanocomposite nitride, carbide or carbonitride hard coating materials, it is understood a multilayered coating where the thickness of each individual nitride, carbide or carbonitride layer is in the nanometer range, usually below 100 nm.
The recent development within tools has been towards sharper cutting edges. This requires thinner coatings in order to maintain the sharp cutting edges. If the coating is too thick, the edge easily gets a more round shape. If a thinner coating is deposited, an increased hardness is required to maintain the wear resistance. One way to achieve a thin hard coating is to use a multilayered nanocomposite coating. In prior art, this nanocomposite coating has usually been deposited onto a homogeneous wear resistant layer.
EP 1 690 959 A discloses a wear resistant coating comprising a single phase structure bottom layer of TiAlSiN having a thickness of from about 2 to about 6 μm and a top layer of a multilayered structure Ti1−(A+B)AlASiBN/Ti1−(C+D)AlCSiDN having a total thickness of from about 0.5 to about 1.5 μm. The composition of the multilayered structure is described with A in the range of from about 0.01 to about 0.06, B in the range of from about 0.25 to about 0.35, C in the range of from about 0.30 to about 0.45 and D in the range of from about 0.1 to about 0.15.
EP 1 702 997 A discloses a hard film for cutting tools composed of Ti1−a−b−c−dAlaCrbSicBd(C1−eNe) where 0.5<a<0.8, b>0.06, c is from about 0 to about 0.1, 0<d<0.1 and 0.5<e<1. The hard film can be in the form of a multilayered structure.
However, further development of multilayered coatings is still required to be able to provide coatings with improved wear resistance while still having a sharp cutting edge.